Process for vacuum coating extruded material

ABSTRACT

Process for the vacuum coating of an extruded material, particularly animal food, in which the extruded material is coated with a flowable coating material during a vacuum phase and under reduced pressure, characterized in that the extruded material, during the vacuum phase, is initially dried and then coated with the coating material.

BACKGROUND OF THE INVENTION

The invention relates to a process for the vacuum coating of an extrudedmaterial, particularly an animal food, in which the extruded material iscoated with a flowable coating material during a vacuum phase and underreduced pressure.

For manufacturing and product-related reasons, in the case of numerousextruded products, particularly in the human and animal food sector, theneed exists not to have certain constituents of the of the finished andproduct, e.g. fatty substances in the mixture to be extruded, but to addthe same only following the extrusion process, so that an extrudedproduct serves as a carrier for the substance to be subsequentlyapplied.

A known procedure consists of providing a product, which can be porousafter extrusion, with desired constituents. The extrusion product isinitially dried and then exposed to a vacuum and is coated under reducedpressure with a coating material, which has a flowable consistency. Atthe end of the vacuum phase the increasing pressure forces the coatingmaterial into any existing pores of the extruded material, so that thelatter has an increased content of e.g., fat, without the latter beingpreponderantly located on the surface and leading to an excessivestickiness of the product. The porous, extruded product consequently inpart mainly serves as a carrier for the flowable material to be added.In this way, at a vacuum of e.g., 200 mbar, fat contents of up to 30 wt.% are obtained in the end product.

It is a disadvantage of this proven coating process that the total costsfor drying and coating are high and also the absorptivity of theextruded product for a coating material is not always adequate, evenwhen using vacuum.

The problem of the present invention is to improve the known coatingprocess in this connection, i.e., in particular to lower the dryingcosts and also bring about increased productivity for the coatingmaterial.

SUMMARY OF THE INVENTION

According to the invention, this problem is solved by a process for thevacuum coating of an extruded material, particularly animal food, inwhich the extruded material is coated with a flowable coating materialduring a vacuum phase and under reduced pressure. The extruded material,during the vacuum phase, is initially dried and then coated with thecoating material. The drying of the extruded material during, instead ofbefore, the vacuum phase surprisingly leads to several advantages.Firstly, the already porous, extruded material expands further as aresult of the evaporation of water during the vacuum phase, so thatpores are produced or the pore volume is increased and a correspondinglyincreased absorptivity for flowable coating material is obtained. Inaddition, in the case of a vacuum, the drying process can be much bettercontrolled than e.g., drying in hot air, because under reduced pressurethere is an evaporation of the inwardly located material areas, whichwould otherwise not be accessible to contact with drying air. As aresult smaller local fluctuations of the moisture content of the productoccur, so that the mean moisture content can be raised approximately 1%,which is obviously associated with a considerable cost saving. As aresult of the extraction of heat in the drying process the extrudedproduct is simultaneously cooled, so that there is no need for aseparate cooling of the material leaving the extruder at a temperatureof approximately 100° C.

The coating material can contain fat and/or water.

Preferably, the extruded material is porous and expands during thevacuum phase.

Preferably, at the start of the vacuum phase the extruded material has atemperature higher than 90° C.

According to a preferred embodiment, at the start of the vacuum phase,the extruded material has a moisture content, related to its dry,weight, of no more than 25 wt. %.

According to an embodiment of the invention, during the vacuum phase,the moisture content of the extruded material is lowered by 6 wt. %,based on the dry weight.

Prior to the start of the vacuum phase, the extruded material can bepredried at normal pressure.

Preferably, after drying and coating, the extruded material has a finalmoisture content of 9 wt. %, based on its dry weight. After drying andcoating, the extruded material preferably has a temperature of 25° C.

During the vacuum phase the pressure can be lowered to 200 mbar.

According to an embodiment, at the start of the vacuum phase thepressure is lowered to 40 mbar. The pressure can be kept at 40 mbaruntil the extruded material reaches a temperature of 30° C. or lower.

The vacuum phase can last up to 5 minutes.

During the vacuum phase, it is possible to supply additional energy,particularly in the form of infrared or microwave radiation.

BRIEF DESCRIPTION OF THE DRAWING

Further advantages and features of the invention can be gathered fromthe following description of preferred embodiments with reference to theattached drawings, wherein:

FIG. 1 Is a graph of the time behavior of product temperature andpressure in an embodiment of the process according to the invention.

FIG. 2 Shows an arrangement for performing the process according to theinvention.

FIG. 3 Is a similar representation to FIG. 1 of time behavior of producttemperature and pressure in a prior art process.

DESCRIPTION OF A PREFERRED EMBODIMENT

Reference is first made to FIGS. 2 and 3 in order to illustrate theknown procedure. A mixture to be extruded passes into the extruder 1,arrow 2, and leaves it at its discharge opening 3 at a temperature ofapproximately 100° C. Based on the dry weight of the extruded product,the moisture content at this point is approximately 25%. The extrudedproduct is then dried in a drier 4. After coating in a mixer 5, it has amoisture content, based on the dry substance, of 9 wt. % and atemperature of 25° C. The moisture content obtained at the drier outletis dependent on the particular coating material used for coating theextruded material in the mixer 5, i.e., on its water content. Forexample, when coating with an aqueous coating material a moisturecontent of 6 wt. % may be necessary at the drier outlet, in order toarrive at a final moisture content of 9 wt. %. Conversely, when coatingwith a coating material containing little or no water, e.g., a fattysubstance, it may be possible to obtain a higher moisture content than9% at the outlet of the drier 4 or on entering the mixer 5. This is sobecause the moisture percentage, based on the dry weight, decreases whenan anhydrous substance is applied.

FIG. 3 illustrates the time sequence of the processes during vacuumcoating within the mixer 5 in accordance with the prior art. Extruded,dried, porous material cooled to approximately 30° C. (below 50° C.) isfilled, under ambient pressure, into mixer 5, whose charging opening isdirected upwards (left-hand mixer representation in FIG. 2). The fillingopening is closed and the internal pressure is lowered within arelatively short time of approximately 1.5 minutes to approximately 200mbar. Previously, subsequently or simultaneously, coating material isfed into the mixer and the extruded materials is mixed therewith. Thepressure in the mixer is then increased again to ambient pressure sothat the coating material is forced deeply into the porous cavities ofthe extruded material. As shown in FIG. 3, throughout the process theproduct temperature remains almost unchanged at approximately 30° C.,which corresponds to the filling or charging temperature.

Compared to this prior art, the process according to the inventiondiffers in that the extruded product, which leaves the extruder 1 at itsdischarge opening with a temperature of approximately 100° C., isinitially not cooled and is passed into the mixer 5 at approximately 95°C. As a result of the unavoidable transporting path the extruded producttemperature decreases by approximately 5° C. This is further illustratedin FIG. 1, which in similar manner to FIG. 3 shows the time behavior ofthe product temperature and pressure during the coating and mixingprocess. It is also pointed out that on the right-hand side of FIGS. 1and 3 is plotted the boiling point of water, which corresponds to thepressure on the left. Thus, 200 mbar correspond to a boiling point ofapproximately 60° C. and 40 mbar to approximately 30° C., etc.

The extruded, porous material passes more or less directly out of theextruder into the mixer, the temperature being almost 100° C. Afterclosing the mixer, the pressure is lowered to approximately 200 mbar, oras shown in FIG. 1, even to 40 mbar. As a result of the boiling pointreduction and the evaporation of the water contained in the extrudedmaterial associated therewith, there is a considerable cooling. Afterthe pressure, whose time behavior is not precisely shown in FIG. 1, hasreached its lowest point of approximately 40 mbar or has stayed for acertain time at this value a moisture content of 19 wt. % still exists.As an example, if in the extruded material at approximately 100° C.there was a moisture content of 25 wt. %, following cooling to 30° C.(boiling point at 40 mbar) as a result of the “vacuum drying” there is amoisture content decrease of 6 wt. % accompanied by a simultaneouscooling to 30° C.

Following such a cooling and drying coating takes places with a desiredmaterial, together with a pressure rise to approximately 200 mbar, theproduct temperature still being 30° C. This and the emptying of themixing vessel (right-hand mixer representation in FIG. 2) substantiallycorrespond to the prior art procedure.

The time pressure distribution, only intimated in FIG. 1, on reducingpressure from ambient pressure to 40 mbar, or at least 200 mbar, isinter alia dependent on the moisture content with which the extrudedmaterial is introduced into the mixer and to what extent drying is totake place, i.e., what type of coating (aqueous or anhydrous) is usedfor coating purposes. The expanding behavior of the extruded materialcan also be influenced by the speed of the pressure drop.

Under the basic assumption that in a specific process sequence in thevacuum phase in the mixer there is always a moisture content reductionby 6 wt. %, without the temperature dropping below 25 to 30° C., e.g.,the following process alternatives are also possible:

1. Extruded material entering the mixer at 16 wt. % moisture and 95° C.,following a pressure drop to 50 mbar, after a certain time, reaches amoisture content of 10 wt. % and a temperature of 25° C. After coatingwith a fat-containing coating material containing little or no water thedesired moisture content of 9 wt. % is reached. The delivery temperatureis in unchanged form 25° C.

2. If the moisture content of the extruded material is higher, it iseither necessary to operate with an external energy supply during thevacuum phase or with predrying before the vacuum phase.

If the moisture content of the extruded material is e.g., 25% andcoating is to take place with an aqueous material, the extruded materialcan initially be predried (at 95° C.) to 12 wt. %, before being driedaccording to the invention during the pressure reduction to 40 mbar to 6wt. % moisture and 25° C. By coating with aqueous material 9 wt. %moisture at 25° C. is obtained.

Alternatively a drying to a higher moisture content, e.g., 16 wt. %,would be adequate, if coating takes place with a material containinglittle or no water. Then, in the mixer, on reducing the pressure, thereis e.g., a 10 wt. % moisture content and a temperature of 25° C. andafter fat coating 9 wt. % moisture at 25° C.

When operating with an initial moisture content of 25 wt. %, withoutpre-drying, energy must be supplied during the vacuum phase,particularly in the form of microwave heating. As a result the desiredvalues of e.g., 6 wt. % moisture at 25° C. are obtained prior tocoating.

As in the case of vacuum drying there are scarcely any localfluctuations of the moisture content or peak values, a very precisemoisture setting occurs, so that the mean value of the moisture contentcan be raised by approximately 1 wt. % compared with the known procedureusing a hot air drier. This is not altered by the fact that in certaincases, according to the invention, it may be appropriate to use a (hotair) predrier, because this merely lowers the overall moisture contentprior to the actual drying stage, whereas the actual “fine setting”takes place during the vacuum phase. Considerable energy savings resultfrom this.

As a result of the time control of the pressure reduction ordistribution, it is possible to influence whether or not the extrudedproduct is to be further expanded. It can be appropriate in some casesto solidify the extruded product in a predrier to such an extent that itdoes not excessively stick.

The features of the invention disclosed in the description, drawings andclaims can be essential to the implementation of the differentembodiments of the invention, either singly or in the form of randomcombinations.

What is claimed is:
 1. A process for the vacuum coating of an extrudedmaterial in which the extruded material is coated with a flowablecoating material during a vacuum phase under reduced pressure whereinthe extruded material is initially dried and then coated with thecoating material and wherein the pressure at the start of the vacuumphase is lowered to 40 millibar and during the vacuum phase the pressureis raised to 200 millibar.
 2. A process for the vacuum coating of anextruded material in which the extruded material is coated with aflowable coating material during a vacuum phase under reduced pressurewherein the extruded material is initially dried and then coated withthe coating material and wherein during the vacuum phase the pressure islowered to 200 millibar and then lowered to 40 millibar and wherein thepressure of 40 millibar is maintained until the extruded material hasreached a temperature of 30° C. or lower.
 3. A process according toclaim 1 or 2 wherein the coating material contains fat and/or water. 4.A process according to claim 1 or 2 wherein the extruded material isporous and expands during the vacuum phase.
 5. A process according toclaim 1 or 2 wherein at the start of the vacuum phase the extrudedmaterial has a temperature of more than 90° C.
 6. A process according toclaim 1 or 2 wherein at the start of the vacuum phase the extrudedmaterial has a moisture content of no more than 25 wt. % based on itsdry weight.
 7. A process according to claim 1 or 2 wherein the moisturecontent of the extruded material is lowered by 6 wt. % based on its dryweight during the vacuum phase.
 8. A process according to claim 1 or 2wherein prior to the start of the vacuum phase the extruded material ispredried at normal pressure.
 9. A process according to claim 1 or 2wherein after drying and coating the extruded material has a finalmoisture content of 9 wt. % based on its dry weight.
 10. A processaccording to claim 1 or 2 wherein after drying and coating the extrudedmaterial has a temperature of 25° C.
 11. A process according to claim 1or 2 wherein during the vacuum phase additional energy is supplied inthe form of microwave energy.